/*
 * Copyright 2015-2022 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.stun4j.stf.core.support;

import java.io.Serializable;

/**
 * Simple serializable class that serves as a {@code null} replacement
 * for cache stores which otherwise do not support {@code null} values.
 * @author Juergen Hoeller
 * @author Jay Meng
 *         <p>
 *         From spring-data-redis:2.6.4,changes listed below
 *         <ul>
 *         <li>Disable all Spring dependency</li>
 *         <li>Change {@code serialVersionUID}</li>
 *         </ul>
 * @since 4.2.2
 */
public final class NullValue implements Serializable {

  /**
   * The canonical representation of a {@code null} replacement, as used by the
   * default implementation of {@link AbstractValueAdaptingCache#toStoreValue}/
   * {@link AbstractValueAdaptingCache#fromStoreValue}.
   * @since 4.3.10
   */
  public static final Object INSTANCE = new NullValue();
  private static final long serialVersionUID = 1L;

  private NullValue() {
  }

  private Object readResolve() {
    return INSTANCE;
  }

  @Override
  public boolean equals(Object obj) {// @Nullable Object obj
    return (this == obj || obj == null);
  }

  @Override
  public int hashCode() {
    return NullValue.class.hashCode();
  }

  @Override
  public String toString() {
    return "null";
  }

}